See, for me, the execution of the changes in Cersei was the problem. They did nothing with her deeper & softer character. By the time they got to her turn as regent, the narrative was treating her like the paranoid megalomaniac of the books. Actually, in season 5, she was generally fairly reasonable with her concerns, it was just that no one in her family was listening. Margaery was actually sexually grooming Tommen and using that influence to control him and separate him from his mother. This is a legitimate concern for Cersei, but the show acted like it was her unhinged inability to share power that is established in the books. That was the whole point of Cersei's line "When you play the game of thrones, you win or you die." It showed how for Cersei, power is a zero-sum equation, where anything anyone else has, is of necessity, a loss for her. The whole point of the feudal system was sharing power, because kings lacked the wherewithal to exert the control of a proper government. She might be over the top in the books, but it's consistent. Her ego and arrogance explains her affair with Jaime & fits with the "Lannisters are worth more" attitude their father has inculcated in them (including his own marriage to a Lannister cousin, rather than to secure an alliance). Her half-assed plots and short-sightedness explains how the only thing she did in response to being discovered by Ned was hope REALLY hard that Robert has a convenient hunting accident. Even getting him drunk requires a bit of luck, because it's just as likely that he would pass out before finding any game, and miss the opportunity for a fatal blunder. Her paranoia explains why she never gave Tyrion any trust while he was acting as Hand, and why she often undermined him, nearly fatally.

The show ignored the villain of the early books, and softened her, then tried to reap the benefit of the later books' errors, especially making the Tyrells' actions wildly out of character and the Faith's policies first of all extremely inconsistent and contrary to their own interests, and secondly, governed more by modern Christian fundamentalism than the concerns of a medieval religion (ie hating alcohol - who did they think made a lot of wine and beer in the middle ages? ). You also need a much more literate population than Westeros is shown to have, to get widespread devotion to the minutiae of doctrine. In any case, it does not make sense for the Faith to prosecute their own allies, or even try Cersei, given how Tommen is basically doing everything the High Sparrow wants. Cersei's adultery casts doubt on the legitimacy of their puppet king! And then the grassroots movement utterly vanishes when Cersei blows up the sept -because we all know that's how religious movements behave when you kill their religious & political leaders. Apparently the Sparrow movement consisted of no more people than could fit inside the Sept of Baelor, and everyone else in Kings Landing is just fine with a woman, who has no claim to the throne, and is the daughter of the man who sacked the city at the end of the Rebellion, taking the throne.

All this stuff worked in the books, because the Sparrow movement built off established events - the devastation (largely wrought by the Lannisters) of the war, and the predation on the common people & religious. The crown's debt to the Faith was firmly established. Cersei creates the vacancy by assassinating the High Septon out of paranoia about what Lancel might have told him, and how Tyrion picked him for the job. Cersei came looking for a blessing for Tommen, the High Sparrow talked around it, but he had issues, because her family were behind the problems that his constituency were concerned with. So he was able to leverage concessions from the crown for martial power in exchange for a gesture of support that costs him nothing to give, and the cancellation of a debt he had limited power to collect. Cersei doesn't sic the Faith on the Tyrells for something as nonsensical and hard to prove as Loras' homosexuality. Not least because the witness would be just as culpable, and his "evidence" is bullshit - yes, he has seen Loras naked, but he has also admitted to being his squire. Squires bathe & dress their knights! Cersei brings charges of treason, that Margaery had cheated on Tommen, and the proof is that she is not a virgin. Except Margaery & Tommen consummated their marriage on the show, so they have nothing. They have Margaery under arrest for perjury and come close to making her do a walk of shame, but Cersei gets to walk and have no more than house arrest for capital crimes?

It's all just a random, nonsensical mess that has no coherence, even if they have the occasional scene that paints Cersei in a slightly more sympathetic light.

By contrast HotD finds motivations and character traits to make the actions and characteristics that were just there in the books work. It shows how Alicent went from being friendly to Rhaenyra to plotting to take her throne. It gets into the dynamics of why the Velaryons remain loyal to the claimant who cuckolded their son, and allow her children to falsely claim inheritance of Corlys' title. It does a great job of explaining the attraction of Criston Cole to Rhaenyra, and the transformation to such an extreme antipathy, better than the maesters' tales of courtly love and legalistic adherence to traditions of male-preference. I can even see a path to explaining how Myseria comes to work for the Blacks and then turns on Daemon. Even the missteps, like Aegon's prophecy, or Alicent's misunderstanding of Viserys work out, I think. The former gives a bit more justification to Viserys & Rhaenyra's sense of entitlement, and the latter can be explained as wishful thinking. It's not like she suddenly did a 180, after all. She was prepped long before that, by Otto's warning that Rhaenyra might have no choice but to act against her & her children to prevent others from using them against her. There isn't much in the story, for all that she's been humanized more, to give much hope that Rhaenyra will be a good queen, so if she can find an excuse to get past the final reservation - Viserys making it abundantly clear to the last that he has never wavered in his choice of successor, she's going to run with it.